Moved Availability.h import to a proper place

Masonry/MASConstraint.h

@@ -6,7 +6,6 @@
 //  Copyright (c) 2013 cloudling. All rights reserved.
 //
 
-#import <Availability.h>
 #import "MASUtilities.h"
 
 /**

Masonry/MASViewConstraint.m

@@ -12,6 +12,7 @@
 #import "MASLayoutConstraint.h"
 #import "View+MASAdditions.h"
 #import <objc/runtime.h>
+#import <Availability.h>
 
 @interface MAS_VIEW (MASConstraints)